The present invention relates generally to an electrolytic cell and, more particularly, to a filter press type electrolytic cell having electrodes with the inter-electrode gap so reduced that the electrolytic voltage can be reduced considerably.
The filter press type electrolytic cell has wide applications in organic material production by electrolysis, inclusive of the production of chlorine and caustic soda by brine electrolysis, seawater electrolysis, etc.
FIG. 4(A) is a schematic representation of a filter press type of bipolar electrolytic cell unit used typically for brine electrolysis; the illustration being a partly cut-away plan view of the electrolytic cell unit shown generally as 41, and FIG. 4(B) a sectional view thereof taken along line A--A of FIG. 4(A).
An anodic-side partition 42 of an electrolytic cell unit 41 is obtained by corrugating or otherwise forming a member selected from a thin film-forming metal such as titanium, zirconium or tantalum and its alloy into a pan form of corrugated thin sheet. Likewise, a cathodic-side partition 43 is obtained by corrugating or otherwise forming a member of iron, nickel, stainless steel or like material into a corrugated thin sheet. These partitions are mounted on an electrolytic cell frame 44. Both the partitions have grooves and ridges that are engaged with each other; the anodic-side partition 42 is provided with grooves 45 and ridges 46, and the cathodic-side partition 43 is provided with similar grooves 47 and ridges 48 at positions where they are engaged within and with the ridges 46 and grooves 45 on the anodic side, respectively.
Neither grooves nor ridges are formed on the portions of the partitions 42, 43 adjacent to the upper, lower, right and left walls of each electrode chamber, thereby defining an electrolyte-circulation path therein. An anode 49 is attached, as by welding, to the ridges of the anodic-side partition 42, said anode being formed by applying an anodically active coating made of an oxide of a metal such as a metal of the platinum group on an expanded metal sheet, a porous sheet, etc. Likewise, a cathode 50 is joined, as by welding, to the ridges 48 of the cathodic-side partition 43, said cathode being formed by applying a cathodically active coating made of a metallic substance such as a metal of the nickel or platinum group to an expanded metal sheet, a perforated sheet, or the like.
A very large current of usually a few tens kiloamperes to a few hundred kiloamperes passes through an electrolytic cell; even slight reductions in the electrolytic voltage make some considerable contribution to power consumption reductions. The performance of the electrolytic cell is estimated by many factors, among which the voltage required for electrolysis becomes a very important element.
The voltage needed for electrolysis depends on electrodes, ion-exchange membranes, electrolytic cell structure, running temperatures, the distance between both electrodes of the electrolytic cell, and other factors, and many proposals have been put forth of improvements in electrodes, ion-exchange membranes, electrolytic cell structure, and running conditions.
Of the factors having an influence on electrolytic voltage, an inter-electrode distance reduction in particular is a vital factor that leads to an electrolytic voltage reduction, and various proposals have been made for reduction of the inter-electrode distance.
In brine electrolysis by ion-exchange membrane techniques using a cation-exchange membrane, it has now been found that it is possible to reduce the electrolytic voltage by reducing the distance between the anode and the cation-exchange membrane. This enables an electrolytic cell to be run, while the cation-exchange membrane is brought in close contact with the anode by a pressure difference produced between the cathodic and anodic chambers by making the pressure in the cathodic chamber higher than that in the anodic chamber.
When the electrolytic voltage is reduced in view of the inter-electrode distance, therefore, it is generally important to reduce the distance between the cathode and the cation-exchange membrane.
A proposal has also been put forth of an electrolytic cell, in which the distances between the anode and the cation-exchange membrane as well as the cathode and the cation-exchange membrane are substantially reduced to zero. Although, depending on the type of the cation-exchange membrane used, close contact of the cathode therewith is not always preferable for the performance of the cation-exchange membrane and electrolysis. In the case of such a cation-exchange membrane, it is required to space the cathode away from the cation-exchange membrane with a certain distance.
In order to bring the cation-exchange membrane in close contact with the cathode or keep them with a very short distance between them, it has been proposed to join the partitions or ribs of the electrolytic cell to the electrodes using expanding and contracting members such as springs.
Either in the case of bringing the cation-exchange membrane in close contact with the cathode or in the case of spacing them away from each other a very short distance, it is required to keep the inter-electrode distance and the distance between the cathode and the ion-exchange membrane with high dimensional accuracy. In the case of an electrolytic cell used for brine electrolysis, etc., which uses a movable electrode having a surface area as large as a few square meters, however, it is very difficult to keep the electrode surface uniformly spaced by means of a member such as a spring. An uncertain inter-electrode distance gives rise to uneven current distribution, and so poses several problems such as a local failure of the electrodes and ion-exchange membranes, the performance of the electrolytic cell being adversely affected.